[PAPILLARY CARCINOMA, THYROID]. Papillary carcinoma is the most common malignancy of thyroid both in adults and in children. Originally described with papillary growth pattern it can have a mixed papillary a follicular growth patterns or an exclusive follicular growth pattern. Thus, the final diagnosis of a papillary carcinoma is based on nuclear features rather than architectural features. This image shows papillary growth pattern represented by finger-like projections lined by neoplastic cells.
[PAPILLARY CARCINOMA, THYROID]. Papillary carcinoma often shows a central scar-like fibrotic area which may entrap neoplastic glands. The fibrous bands may extend outward and divide the tumor into large clusters. A tumor capsule may be present in 10-15% of cases especially follicular variant of papillary carcinoma. Intracystic papillary carcinomas are encapsulated and usually show classical papillary architecture.
[PAPILLARY CARCINOMA, THYROID]. A classic papillary carcinoma shows multiple finger-like branching papillary projections (arrows) lined by neoplastic cells. The papillary architecture can be complex with thick fibrovascular cores.
[PAPILLARY CARCINOMA, THYROID]. Branching papillary fronds are seen in this image. A metastatic papillary carcinoma may retain its papillary architecture or may show both follicular and papillary architecture.
[PAPILLARY CARCINOMA, THYROID]. The final diagnosis of papillary thyroid carcinoma is based upon diagnostic nuclear features which include enlarged nuclei, nuclear overlapping, nuclear clearing, nuclear contour angulations, peripheral condensation of nuclear chromatin, nuclear grooves, and nuclear pseudo-inclusions. Not all nuclear features can be evident in all cases. Nuclear grooves are shown with long arrows in this case. The central vascular core is shown with arrowheads.
[PAPILLARY CARCINOMA, THYROID]. A nuclear pseudo-inclusion is shown with an arrow and two nuclear grooves are shown with curved arrows. Note also nuclear overlapping and angulated nuclear contours.
[PAPILLARY CARCINOMA, THYROID]. Papillary carcinoma can have a “follicular” architecture and must be distinguished from a follicular adenoma, follicular carcinoma, and hyalinizing trabecular adenoma. In papillary carcinoma thick-appearing colloid is common in follicular lumens. Note the fibrous trabecular separating large clusters of neoplastic follicles.
[PAPILLARY CARCINOMA, THYROID]. Note thick colloid in small follicles lined by cells with “nuclear features” of a papillary carcinoma such as ground-glass nuclei, nuclear crowding, and angulated nuclear contours. This “follicular variant” of papillary carcinoma is more common than expected of a variant. Immunohistochemistry may help in differentiating a true follicular carcinoma from follicular variant of papillary carcinoma.
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